274 lines
8.8 KiB
Python
274 lines
8.8 KiB
Python
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import ctypes
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from . import opus
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from .pyogg_error import PyOggError
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class OpusDecoder:
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def __init__(self):
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self._decoder = None
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self._channels = None
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self._samples_per_second = None
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self._pcm_buffer = None
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self._pcm_buffer_ptr = None
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self._pcm_buffer_size_int = None
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# TODO: Check if there is clean up that we need to do when
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# closing a decoder.
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#
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# User visible methods
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#
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def set_channels(self, n):
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"""Set the number of channels.
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n must be either 1 or 2.
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The decoder is capable of filling in either mono or
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interleaved stereo pcm buffers.
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"""
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if self._decoder is None:
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if n < 0 or n > 2:
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raise PyOggError(
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"Invalid number of channels in call to "+
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"set_channels()"
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)
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self._channels = n
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else:
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raise PyOggError(
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"Cannot change the number of channels after "+
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"the decoder was created. Perhaps "+
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"set_channels() was called after decode()?"
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)
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self._create_pcm_buffer()
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def set_sampling_frequency(self, samples_per_second):
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"""Set the number of samples (per channel) per second.
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samples_per_second must be one of 8000, 12000, 16000,
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24000, or 48000.
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Internally Opus stores data at 48000 Hz, so that should be
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the default value for Fs. However, the decoder can
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efficiently decode to buffers at 8, 12, 16, and 24 kHz so
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if for some reason the caller cannot use data at the full
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sample rate, or knows the compressed data doesn't use the
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full frequency range, it can request decoding at a reduced
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rate.
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"""
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if self._decoder is None:
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if samples_per_second in [8000, 12000, 16000, 24000, 48000]:
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self._samples_per_second = samples_per_second
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else:
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raise PyOggError(
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"Specified sampling frequency "+
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"({:d}) ".format(samples_per_second)+
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"was not one of the accepted values"
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)
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else:
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raise PyOggError(
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"Cannot change the sampling frequency after "+
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"the decoder was created. Perhaps "+
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"set_sampling_frequency() was called after decode()?"
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)
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self._create_pcm_buffer()
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def decode(self, encoded_bytes: memoryview):
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"""Decodes an Opus-encoded packet into PCM.
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"""
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# If we haven't already created a decoder, do so now
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if self._decoder is None:
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self._decoder = self._create_decoder()
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# Create a ctypes array from the memoryview (without copying
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# data)
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Buffer = ctypes.c_char * len(encoded_bytes)
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encoded_bytes_ctypes = Buffer.from_buffer(encoded_bytes)
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# Create pointer to encoded bytes
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encoded_bytes_ptr = ctypes.cast(
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encoded_bytes_ctypes,
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ctypes.POINTER(ctypes.c_ubyte)
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)
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# Store length of encoded bytes into int32
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len_int32 = opus.opus_int32(
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len(encoded_bytes)
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)
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# Check that we have a PCM buffer
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if self._pcm_buffer is None:
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raise PyOggError("PCM buffer was not configured.")
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# Decode the encoded frame
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result = opus.opus_decode(
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self._decoder,
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encoded_bytes_ptr,
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len_int32,
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self._pcm_buffer_ptr,
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self._pcm_buffer_size_int,
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0 # TODO: What's Forward Error Correction about?
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)
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# Check for any errors
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if result < 0:
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raise PyOggError(
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"An error occurred while decoding an Opus-encoded "+
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"packet: "+
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opus.opus_strerror(result).decode("utf")
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)
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# Extract just the valid data as bytes
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end_valid_data = (
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result
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* ctypes.sizeof(opus.opus_int16)
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* self._channels
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)
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# Create memoryview of PCM buffer to avoid copying data during slice.
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mv = memoryview(self._pcm_buffer)
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# Cast memoryview to chars
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mv = mv.cast('c')
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# Slice memoryview to extract only valid data
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mv = mv[:end_valid_data]
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return mv
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def decode_missing_packet(self, frame_duration):
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""" Obtain PCM data despite missing a frame.
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frame_duration is in milliseconds.
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"""
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# Consider frame duration in units of 0.1ms in order to
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# avoid floating-point comparisons.
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if int(frame_duration*10) not in [25, 50, 100, 200, 400, 600]:
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raise PyOggError(
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"Frame duration ({:f}) is not one of the accepted values".format(frame_duration)
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)
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# Calculate frame size
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frame_size = int(
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frame_duration
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* self._samples_per_second
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// 1000
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)
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# Store frame size as int
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frame_size_int = ctypes.c_int(frame_size)
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# Decode missing packet
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result = opus.opus_decode(
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self._decoder,
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None,
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0,
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self._pcm_buffer_ptr,
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frame_size_int,
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0 # TODO: What is this Forward Error Correction about?
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)
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# Check for any errors
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if result < 0:
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raise PyOggError(
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"An error occurred while decoding an Opus-encoded "+
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"packet: "+
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opus.opus_strerror(result).decode("utf")
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)
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# Extract just the valid data as bytes
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end_valid_data = (
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result
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* ctypes.sizeof(opus.opus_int16)
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* self._channels
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)
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return bytes(self._pcm_buffer)[:end_valid_data]
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#
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# Internal methods
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#
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def _create_pcm_buffer(self):
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if (self._samples_per_second is None
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or self._channels is None):
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# We cannot define the buffer yet
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return
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# Create buffer to hold 120ms of samples. See "opus_decode()" at
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# https://opus-codec.org/docs/opus_api-1.3.1/group__opus__decoder.html
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max_duration = 120 # milliseconds
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max_samples = max_duration * self._samples_per_second // 1000
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PCMBuffer = opus.opus_int16 * (max_samples * self._channels)
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self._pcm_buffer = PCMBuffer()
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self._pcm_buffer_ptr = (
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ctypes.cast(ctypes.pointer(self._pcm_buffer),
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ctypes.POINTER(opus.opus_int16))
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)
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# Store samples per channel in an int
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self._pcm_buffer_size_int = ctypes.c_int(max_samples)
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def _create_decoder(self):
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# To create a decoder, we must first allocate resources for it.
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# We want Python to be responsible for the memory deallocation,
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# and thus Python must be responsible for the initial memory
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# allocation.
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# Check that the sampling frequency has been defined
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if self._samples_per_second is None:
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raise PyOggError(
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"The sampling frequency was not specified before "+
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"attempting to create an Opus decoder. Perhaps "+
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"decode() was called before set_sampling_frequency()?"
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)
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# The sampling frequency must be passed in as a 32-bit int
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samples_per_second = opus.opus_int32(self._samples_per_second)
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# Check that the number of channels has been defined
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if self._channels is None:
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raise PyOggError(
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"The number of channels were not specified before "+
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"attempting to create an Opus decoder. Perhaps "+
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"decode() was called before set_channels()?"
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)
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# The number of channels must also be passed in as a 32-bit int
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channels = opus.opus_int32(self._channels)
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# Obtain the number of bytes of memory required for the decoder
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size = opus.opus_decoder_get_size(channels);
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# Allocate the required memory for the decoder
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memory = ctypes.create_string_buffer(size)
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# Cast the newly-allocated memory as a pointer to a decoder. We
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# could also have used opus.od_p as the pointer type, but writing
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# it out in full may be clearer.
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decoder = ctypes.cast(memory, ctypes.POINTER(opus.OpusDecoder))
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# Initialise the decoder
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error = opus.opus_decoder_init(
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decoder,
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samples_per_second,
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channels
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);
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# Check that there hasn't been an error when initialising the
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# decoder
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if error != opus.OPUS_OK:
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raise PyOggError(
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"An error occurred while creating the decoder: "+
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opus.opus_strerror(error).decode("utf")
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)
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# Return our newly-created decoder
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return decoder
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